Building first floor extension on existing extension

[yorkshirepudding]

We have an existing ground floor (flat roofed) extension to our 1900s terrace house. The extension was built in the 1970s/80s and utilises some walls from an earlier extension to the house. We are wanting to build a first floor extension on top of this to give us two more bedrooms and a showeroom.

Our next door neighbour is in the exact same position except they are further ahead with planning than we are. They have been told that if when the roof is taken off and the walls are exposed, they are only solid walls, an RSJ will be needed and the outer-wall will need to be inset by 9 inches.

I know that the back wall is cavity as it was checked when I had the kitchen done. However, I don't know about the side walls and am concerned about potentially losing 18" of the length of the extension.

Can anyone clarify whether this is correct and if so, why? I can understand the RSJ but not insetting the wall.

Also, if my neighbour and I are putting the extensions up at the same time and therefore the adjoining wall will be a party wall, do we each need a separate cavity wall?

I would be grateful for any advice or pointers on this subject.

Cheers
yorkshirepudding

 

[noseall]

9in or 225mm solid walls can be made into regulation 280mm cavity walls(when building on top) by using 270mm wide x 6mm galvanized steel plate, provided conditions allow. hope this helps!

 

[chappers]

and no you don't need seperate cavity walls but you need a party wall agreement.

 

[yorkshirepudding]

Thanks. That's very interesting - I'll look further at the party wall agreement to see if we can do it.

Cheers

 

[peca27]

how is a party wall agreement done? is it just between the neighbours or does something official thru the council has to be done????

 

[HandyJon]

A party wall agreement is ususally arranged through a solicitor, though in theory you could arrange one between yourselves but not advisable. It's basicaly a document that details the procedures if something goes wrong, allows you to go on your neighbours land if necessary, and says what can be done and what not and what costs are shared and what are not.

See the Act itself here - http://www.opsi.gov.uk/acts/acts1996/1996040.htm